This invention relates to the use of metallised sheet-form textiles for the wide-band screening of microwave and high-frequency radiation in the range from 0.01 to 100 GHz.
By virtue of advances in hardware, coupled with the fact that microwaves can conveniently be concentrated, it is now possible to achieve power densities of 10 W/cm.sup.2 in microwave radiation. In many new fields of application, radiation protection against high-frequency electromagnetic alternating fields has also increased in significance (P. Brodeur "The Zapping of America", W. W. Norton & Co., Inc., New York 1977). A radiation dose to the human body of from 10 to 20 mW/cm.sup.2 is regarded as the upper limit. It has also been recommended that, in the event of long-term irradiation, the radiation dose should not exceed 1 mW/cm.sup.2.
Accordingly, there is a need for screening materials which are capable of attenuating the electromagnetic waves by 30 to 40 dB. In the case of measuring instruments, even higher attenuation may be necessary. The frequency range of the microwave systems mostly used today extends from 1 to 30 GHz. Accordingly, microwave radiation up to 1000 GHz is likely to be used.
Basically, microwaves can be screened on passage through a compact metallic material. However, it is precisely for protecting human beings against radiation and for special technical applications that it is desirable to have a lightweight flexible screening material. Even a fabric of pure metal filaments is heavy and inflexible. Knitted fabrics cannot be produced from metal filaments.